As a conventional stroboscopic device, a zoom strobe capable of changing the irradiation angle in accordance with the focal length of a lens, i.e., the photographing angle of view has been put into practical use. In addition, a zoom strobe by which a camera outputs focal length information of an attached lens to a stroboscopic device, and, on the basis of this information, the stroboscopic device automatically changes and sets the irradiation angle to an optimum value has been put into practical use.
When the irradiation angle is to be automatically set to an optimum value on the basis of focal length information of a lens, it can be unconditionally done if the aperture size of a camera to which this stroboscopic device is attached is always constant. If this is not the case, i.e., if the stroboscopic device can also be attached to a camera having a different aperture size, the irradiation angle cannot be simply set to an optimum value on the basis of only the focal length information of the lens.
The irradiation angle of a stroboscopic device must be determined in accordance with the photographing angle of view. Therefore, when a stroboscopic device is attachable to cameras different in frame size, the irradiation angle cannot be set to an optimum value on the basis of only focal length information of a lens.
To solve this problem, a method by which a camera. outputs focal length information of a lens and frame size information of the camera, and the irradiation angle of a strobe is adjusted on the basis of these pieces of information is proposed (e.g., Japanese Patent Laid-Open No. 8-6120).
In another method (e.g., Japanese Patent Laid-Open No. 5-313230), the movement and light distribution angle of a strobe light-emitting portion are changed in accordance with the width and moving velocity of a shutter slit so that a stroboscopic device which emits light in synchronism with the start of exposure of a focal-plane shutter irradiates only the region of an object to be photographed in the region of the slit width, thereby emitting light by effectively using the overall light amount of the strobe.
In still another method (e.g., Japanese Patent Laid-Open No. 6-11760), the strobe irradiation angle can be selected in accordance with the focal length of a lens, so a photographer can easily get a photographing image because he or she can set the irradiation angle before photography.
In still another method (e.g., Japanese Patent Laid-Open No. 5-11315), if no focal length information of a lens is obtained, a photographing failure caused by vignetting of distributed light is prevented by forcedly changing the irradiation angle of a strobe to a wide angle.
In Japanese Patent Laid-Open No. 8-6120, a correct strobe light distribution angle is set by transmitting focal length information of a lens and image size information from the camera to the stroboscopic device. However, if the number of variable steps of the strobe irradiation angle increases, the process of conversion from the focal length and image size into the light distribution angle performed by arithmetic processing in the stroboscopic device is complicated.
In Japanese Patent Laid-Open No. 5-313230, operation coefficients are preset in the strobe, and an operation is performed by finding an operation coefficient from the image size. However, since the movement and light distribution angle of the strobe light-emitting portion are changed in accordance with the width and moving velocity of the shutter slit so that the stroboscopic device which emits light in synchronism with the start of exposure of the focal-plane shutter irradiates only the region of an object to be photographed in the region of the slit width, the mechanism is complicated, and the tracking control of synchronous communication when the shutter speed is high is a problem.
In Japanese Patent Laid-Open No. 6-11760, a photographer can easily get a photographing image by setting the strobe irradiation angle before photography. However, the user himself or herself must manually change the light distribution angle.
In Japanese Patent Laid-Open No. 5-11315, if no focal length information of a lens is obtained, a photographing failure caused by vignetting of distributed light is prevented by forcedly changing the irradiation angle of the strobe light to a wide angle. However, the irradiation angle is not particularly changed in accordance with a difference between aperture sizes.
Furthermore, a system in which a plurality of stroboscopic devices are arranged around an object, and light emission and the like of these devices are controlled by wireless transmission/reception is recently proposed.
In this system, for example, a stroboscopic device attached to a camera is a master strobe, and other stroboscopic devices are slave strobes. Appropriate stroboscopic photography of an object can be performed by adjusting the light amounts of the slave strobes by a transmission signal from the master strobe. Since the irradiation angle of each slave strobe is desirably set at a wide angle so that an object is well irradiated with light, this irradiation angle is automatically set at a wide angle in the slave mode.
Unfortunately, if the master strobe is detached from the camera and used as a slave strobe, the last-set irradiation angle sometimes remains because the last settings cannot be canceled.